Various approaches for destroying or eliminating volatile organic compounds (VOCs) have been proposed. U.S. Pat. No. 5,650,128 notes the type of treatment chosen has generally depended on the composition and concentration of the VOCs. For example, in cases where the concentration and/or the boiling point of the VOCs are low, condensation is economically impractical as compared to the capital and operating costs of adsorption or oxidation. But, U.S. Pat. No. 5,650,128 notes that one problem in many VOC abatement situations is that the concentration of VOCs will vary over time. U.S. Pat. No. 5,650,128 further notes that, for high VOC loadings, thermal oxidizers are typically preferred due to their ability to withstand high temperatures, and their low operating cost and high destruction rate. For low VOC loadings, catalytic oxidizers are typically preferred due to their lower operating temperature, which requires very little supplemental fuel addition. Conversely, when a thermal oxidizer is operated on low VOC concentrations, high fuel consumption is required to maintain the high temperatures required by the oxidizer. When a catalytic oxidizer is operated on high VOC concentrations, potential catalyst sintering and deactivation can result due to excessive temperatures.
U.S. Pat. No. 5,650,128 notes that attempts have been made to overcome this operating cost/burnout scenario by creating systems that utilize both a thermal oxidizer and a catalytic oxidizer, but such systems typically have the two oxidizers as separate entities with some sort of mechanism for switching from one unit to another depending upon VOC concentration. One example of such a dual system is shown in U.S. Pat. No. 4,983,364 (Buck et al.) but such dual, segregated systems result in high capital costs.
U.S. Pat. No. 5,427,746 notes that a conventional thermal oxidizer can operate at temperatures in excess of 1,400 degree F. and convert over 99% of the VOCs. However, it is noted, the exhaust can contain nitrogen oxide (NOx) formed in the burner—and carbon monoxide (CO)—a product of incomplete combustion). This is disadvantageous in that environmental regulations are requiring increasingly stringent controls on VOC, CO and NOx emissions. U.S. Pat. No. 5,427,746 notes, for example, that European regulations are requiring the control of VOC levels below 20 mg/Nm3, and control of CO and NOx levels below 50 mg/Nm3.
U.S. Pat. No. 5,673,553 discloses a system for the destruction of VOCs comprising a combustor and a reaction chamber operable to destroy VOCs by combustion. However, the need still exists for a VOC approach which can balance the feed of VOCs from one or multiple sources in a manner which ensures safe and reliable feed of the VOCs. Moreover, in the event that a VOC destruction arrangement includes sensing capability to sense properties of the VOCs contributed by the various VOC sources, such a VOC contributor sensing system should preferably be inexpensive to manufacture and should be capable of using a power source that is readily available in a typical process plant, in order to keep installation costs to a minimum. The system should be suitable for use in harsh environments, including areas subject to spray washing, high humidity, high and low temperatures, and vibration. The system also should be simple and reliable, in order to keep maintenance costs to a minimum.
Accordingly, it is an object of the present invention to provide an apparatus and method that addresses the concerns set forth above.